In recent years, a technique called projection mapping, in which a video is projected onto an object placed in the real world using a video display device such as projector, has attracted public attention.
By using this technology, it is possible to project a video onto a screen which is placed at an angle without directly facing the projector, an uneven object, or the like in addition to a flat screen directly facing the projector. In a case in which a projection target such as screen does not face the projector directly, that is, in a case in which an optical axis of the projector and a projection target surface do not intersect at a right angle, geometric distortion occurs in a projected video. For example, in a case in which a screen is installed such that an upper side of the screen is close to the projector, and a lower side of the screen is far from the projector, if a square video is projected from the projector, so-called trapezoidal distortion in which the upper side of the square is projected shorter than the lower side occurs. In practice, since a similar phenomenon occurs not only in a vertical direction but also in a left and right direction, the square video projected from the projector is projected as a distorted rectangle having no parallel sides.
In this case, reverse geometric correction is applied to a video to be projected to cancel the distortion, and it is possible to correctly display the video in the square shape. The geometric correction (geometric transform) is called perspective transformation or projection transformation and can be implemented through a matrix calculation.
In order to calculate the matrix, it is necessary to acquire information related to a shape and a position of a projection object through a certain means.
A method for implementing this is disclosed in JP 2005-37771 A (Patent Document 1). In Patent Document 1, a shape of a projection target is acquired by projecting a grid using infrared light from a projector and performing photographing through an infrared camera.